Interesting article.

A friendly heads up that I think there's a subtle race condition in your getArticleTypeById. It loads in everything from article_types, but it is invoked by map -- so it could be called many times in close succession.

The problem is that the cache local variable is set only after querying article_types, so this means that it's possible to have multiple Postgres queries outstanding. I suppose you're using a pool, so the impact will be limited by the pool size. However, it would mean that the entire pool could be temporarily exhausted before the cache is built and set.

Perhaps one way to fix it would be to make cache a Promise<Map<...>> instead of just a Map<...>. Something like this:

const buildCache = async () => {....};
if (!cache) {
  // note: no await here - we want the promise
  cache = buildCache(); 
}
return (await cache).get(id);

There's something similar in your Outbox pattern blog post too - awaiting on connect() between checking the CURSOR_REPO_MAP and updating the CURSOR_REPO_MAP, so not 100% guaranteeing a singleton.